1. Field of the Invention
The present invention relates to a liquid crystal display apparatus provided with an electromagnetic-induction touch panel, and more particularly relates to a liquid crystal display apparatus incorporated in a mobile information terminal apparatus, a tablet personal computer, or another information processing apparatus.
2. Description of the Related Art
Display apparatuses having a touch panel are provided with both image display and information input functions, and are currently widely used in ATMs (automated teller machines) for financial institutions and in other equipment. In particular, electromagnetic-induction touch panels that detect electromagnetic energy generated in the panel by a dedicated pen can be operated only with this pen, even when the pen does not make direct contact with the panel. The panel can therefore be disposed further rearward from the liquid crystal panel. For this reason, liquid crystal display apparatuses provided with an electromagnetic-induction touch panel can easily be made smaller and thinner, and can be applied to tablet PCs (Personal Computer), PDAs (Personal Digital Assistant), and other personal information processing devices (Japanese Laid-open Patent Application No. 2004-280273 and Japanese Laid-open Patent Application No. 2004-302431).
FIG. 1 is an exploded perspective view of a portion of the configuration of a conventional liquid crystal display apparatus having a touch panel. In the conventional liquid crystal display apparatus having a touch panel 100, an electromagnetic-induction touch panel 102 in which, for example, a coil is formed on a glass epoxy substrate is disposed on a shield plate 107, and a light guide plate 105 and a liquid crystal panel 101 are disposed in the stated order on the touch panel 102, as shown in FIG. 1. A backlight interface (also referred to as I/F) flexible printed circuit (FPC) substrate 106 is bonded to the end portion of the light guide plate 105, and LEDs (Light Emitting Diode) 104 used as light sources for the backlight are mounted on the backlight I/F FPC substrate 106. Power is fed to the LEDs 104 via the backlight I/F FPC substrate 106. A touch-panel I/F FPC substrate 103 is connected to the touch panel 102 in order to feed power and signals to the touch panel 102, and a liquid crystal panel I/F FPC substrate 108 is connected to the liquid crystal panel 101 in order to feed power and signals to the panel.
Disclosed in Japanese Laid-open Patent Application No. 2004-280273 is a liquid crystal display apparatus having a touch panel in which the surface of the liquid crystal panel is provided with a hard layer composed of material that is harder than the touch pen in order to prevent damage to the areas with which the touch pen (dedicated pen) makes contact. In the liquid crystal display apparatus having a touch panel described in Japanese Laid-open Patent Application No. 2004-302431, the apparatus is made thinner by forming a group of transparent electrode coils for the touch panel on one of the substrates of the liquid crystal panel.
However, the prior art described above has the following problems. In a conventional small liquid crystal display apparatus, LEDs are commonly used as the light source, and an FPC on which a plurality of LEDs are mounted is fixed to the light guide plate. For this reason, in a conventional liquid crystal display apparatus 100 that has a touch panel and is configured in the manner shown in FIG. 1, the backlight I/F FPC substrate 106 on which the LEDs 104 are mounted is easily deformed by pressure applied by the touch pen when information is input, and there is a problem in that brightness nonuniformity is readily produced in the display image. This problem can be improved by fixing the LEDs 104 to the light guide plate 105 (see Japanese Laid-open Patent Application No. 2004-173302, for example), but this approach is still disadvantageous in that manufacturing costs increase due to the greater number of components and manufacturing steps.